Conventionally, it is well known that a bonnet for covering an engine and a battery disposed in the front side of a tractor can be made to open or close around the front side of the vehicle. Alternatively, a rear fulcrum and a locking device can be provided at the side opposite to the rotary fulcrum of the bonnet. For example, Japanese Utility Model Laid-Open Gazette No. Sho. 57-88858 discloses that the bonnet can open or close using the front portion as the fulcrum. At the rear of the bonnet, a one-sided control member, connected to a left and a right retaining member by a left and a right link, can release the lock. Also, Japanese Utility Model Laid-Open Gazettes Nos. Sho 61-90672, Sho 63-51064, Hei 3-24978 and Hei 5-80973, disclose that the front of a bonnet can be made to open or close using the rear portion as the fulcrum. A controlling knob can be provided with an engaging portion provided under or inside thereof, above the center of the front of the bonnet or at the center of the front surface, so that the controlling knob is operated to release the lock.
However, where the rotary fulcrum is provided at the front of the bonnet, and the battery is disposed at the front of the engine space, when the battery is changed or maintenance work is performed, in order to remove the battery, a worker must raise the bonnet while avoiding contact between the battery and the bonnet, or he must put his head into a restricted space while working, thereby making the work difficult to carry out. Where the rotary fulcrum is provided at the rear of the bonnet, the radiator must be raised and removed in order to perform maintenance of the battery. Also, where the lock control member or the locking device is positioned at the center of the front of the bonnet, the front of the bonnet is raised, to ensure that there is space to dispose the locking device around a headlight, thus narrowing the field of view and causing the bonnet to be larger.